The present invention relates to a disposable diaper having front and rear waist regions connected to each other by a fastener means when the diaper is put on.
In Japanese Unexamined Patent Application Publication No. 2000-254176 (hereinafter referred to as “Citation”), there has already been proposed a disposable diaper composed of, in a longitudinal direction, a front waist region, a rear waist region and a crotch region extending between these waist regions and comprises a liquid-pervious topsheet, a liquid-impervious backsheet and a liquid-absorbent core interposed between these two sheets. The diaper is contoured by longitudinally opposite ends extending in a transverse direction outside longitudinally opposite ends of the core and transversely opposite side edges extending in the longitudinal direction outside transversely opposite ends of the core and wherein first wings extend outward in the transverse direction from respective side edges of the front waist region and second wings extend outward in the transverse direction from the respective side edges of the rear waist region.
In the diaper disclosed in Citation, band-like first elastic members extending in the transverse direction is contractibly attached to the longitudinally opposite ends of the front and rear waist regions, respectively, and a plurality of strand-like second elastic members extending in the transverse direction are contractibly attached to the rear waist region so as to lie between the end of the core and the first elastic member in the rear waist region. In this diaper, the second elastic members extend between the transversely opposite side edge portions and further into wings. The wings of the rear waist region are elastically stretchable in the transverse direction. Each of the tape fasteners has a fixed portion permanently bonded to the associated wing of the rear waist region and a free portion extending outward from the fixed portion in the transverse direction. Hooks constituting a so-called mechanical fastener are attached to the free portion of the tape fastener and a stretch stress higher than those of the inner layer sheet and the outer layer sheet. Each of the tape fastener has a fixed side portion which is permanently bonded to outer end of the associated second wing and a free portion extending outward from the fixed side portion in the transverse direction. Hooks constituting a so-called mechanical fastener are attached to the free portion.
An example of the sequence in accordance with which a parent or a care personnel puts the diaper on the wearer's body will be described. After the hip of the wearer lying face up has been laid on the developed diaper, the front waist region is held with the hand and folded back along the crotch region onto the wearer's belly. Then, with the tape fasteners gripped by the fingers, the wings of the rear waist region are folded back so that these wings are placed on respective outer sides of the wings of the front waist region. Adjusting a tightness of the end portions as well as of the wings around the wearer's waist, the free portions of the respective tape fasteners are alternately anchored on the outer surface of the front waist region. Upon connection of the front and rear waist regions to each other, the diaper is formed with a waist-hole and a pair of leg-holes.
In the case of the diaper disclosed in Citation, the second elastic members are stretched in the transverse direction and thereby the wings of the rear waist region also are stretched in the transverse direction as the tape fasteners are pulled outward in the transverse direction when the diaper is put on. A tensile force exerted on the second elastic members is transmitted to the first elastic member which is, in turn, stretched in the transverse direction and thereby the end portion of the rear waist region is stretched in the transverse direction.
In this diaper, the first and second elastic members may often different stretch stresses since the first elastic members are band-like and the second elastic members are strand-like. With a consequence, a transverse stretch stress of the end portion of the rear waist region along which the first elastic member extends may often be different from a transverse stretch stress of the wings of the rear waist region along which the second elastic members extend.
If the wings of the rear waist region exhibit a transverse stretch stress higher than a transverse stretch stress exhibited by the end of the rear waist region, the end of the rear waist region will be fully stretched before the wings should be sufficiently stretched. If the free portions of the respective tape fasteners are anchored on the front waist region at this moment, the diaper will be put on the wearer's body with the wings insufficiently stretched in the transverse direction. Consequently, the contractile force of the wings can not be utilized to ensure a desired tightness of the diaper around the waist of the wearer and the diaper may slip down from the proper position at which the diaper should be held on the wearer's body. In addition, the end portion of the rear waist region may locally constrict the wearer's waist and the wearer may experience uncomfortable feeling of local oppression.